The present invention relates to aqueous adhesive compositions curable at room temperature and more particularly to an improved aqueous latex adhesive composition possessing improved water resistance and being especially adapted for use in structural lamination manufacture.
Various forms of plywood have found utility as structural or load-bearing components in the construction industry. While urea resins, melamine-urea co-condensation resins and phenol resins initially predominated as the adhesives of choice in plywood manufacture, aqueous-based adhesives have more recently found general acceptance in plywood manufacture. Aqueous adhesives can reduce the amount of organic volatiles released from the adhesive composition upon drying and generally possess less organic material which can be released by the adhesive during use of the laminates over time. The reduction of water-sensitivity of the aqueous adhesives, however, was an initial concern of laminate manufacturers. This problem has been addressed by the art and several solutions proposed.
The solution germane for present purposes is the protected-isocyanate approach disclosed in U.S. Pat. No. 3,931,088. The water-resistant adhesive reported therein consists of an aqueous SBR or similar latex and an isocyanate dispersed in a hydrophobic solution of organic solvent. The latex, the surfactant associated with the latex, or an added ingredient bears active-hydrogen groups for linking with the isocyanate at room or elevated temperature. While such adhesive composition has advanced practical use of aqueous latex adhesives in structural lamination production, improvement for room temperature curable adhesive compositions having improved water resistance still has been needed. Such need is addressed by the improved latex adhesive composition disclosed herein.